India has sighted more than a dozen Chinese warships in the Indian Ocean in the last two months. China says the ships are involved in anti-piracy patrols and are moving in international waters.

Border guards of India and China are in a tense standoff along the Sikkim border. (HT file photo)

Anti-piracy patrols and freedom of navigation are the reasons cited by China for its increased presence in the Indian Ocean, forcing New Delhi to tighten surveillance of the strategic waters, government sources have said.

Beijing has raised the pitch and its media are warning of a war, demanding India withdraw its troops from the Doklam, a disputed region.

The increased presence of Chinese warships coincides with the Sikkim standoff but the trend had remained the same for several months, navy officials said.

The Chinese deployment in the pirate-infested Gulf of Aden, one of the world’s most important shipping routes, accounts for four to five warships at any given time.

The periodic rotation of these units gave the Chinese navy the opportunity to deploy a variety of assets in the region, officials said. “Chinese submarines have been spotted in the region. Such assets are not used for anti-piracy operations. They are clearly making their presence felt in the region,” a naval officer said on condition of anonymity as he is not authorised to speak to media.

The Indian Navy has been present in the Gulf of Aden since October 2008 and so far, 64 warships have been involved in anti-piracy operations.

The officials said China has been deploying submarines in the Gulf of Aden regularly since 2014. “The pattern is they deploy a submarine for three months followed by a three-month break,” the officials said.

The imminent commissioning of a Chinese base and support facility at Djibouti in Horn of Africa will boost Beijing’s ability to sustain naval units in the Indian Ocean.

Sources said Chinese navy research vessels have been mapping the region for both military and economic purposes. The presence of submarines has been confirmed through the sighting of Chinese navy’s submarine support vessels.

Sources said Chinese intelligence-gathering ships would be prowling the Indian Ocean to track Malabar, an international naval exercise involving the US, India and Japan. The week-long exercise begins July 10.

India is using its satellites, P-8I maritime surveillance aircraft and surface ships to keep a track of the “unusual surge” in Chinese activity in the Indian Ocean, the sources said.